Wireless communication systems, such as cellular voice and data networks, typically include multiple wireless access nodes spread over a geographic area. As a result, wireless communication devices can register at various wireless access nodes and access communication services. In many examples, the wireless communication devices are mobile, and can move between wireless coverage areas of the wireless access nodes.
The Long Term Evolution (LTE) protocol (also known as Evolved Universal Terrestrial Radio Access Network, or E-UTRAN) is a wireless communication protocol developed from GSM and 3GPP cellular communication standards. LTE is the first GSM/3GPP standard that is fully IP and packet-based, and can be fully integrated into 2G and 3G cellular infrastructure.
LTE was developed to provide improved performance and better spectral efficiency to cellular networks. LTE supports high data rates for services such as voice over IP (VOIP), streaming multimedia, videoconference, and high-speed cellular modem services. LTE supports flexible carrier bandwidths as well as Time Division Duplex (TDD) and Frequency Division Duplex (FDD) communication modes. LTE was designed with a scalable carrier bandwidth from 1.4 megahertz (MHz) to up to 20 MHz. The bandwidth that is used depends on the frequency band and the amount of spectrum available to a network operator.
LTE uses the concept of a Resource Block (RB), which is a block of 12 subcarriers in one slot. A transport block is a group of RBs with a common modulation/decoding. The physical interface is a transport block, which corresponds to the data carried in an allocated period of time for a particular wireless device in communication with a wireless communication network.
LTE typically assigns communication resources to a User Equipment (UE) in units of one RB, which has a bandwidth of 180 kilohertz (KHz). Each RB contains twelve Resource Elements (REs). The minimum transmit time range for LTE is the transmit time interval (TTI), which equals one millisecond (ms). For a voice-over-LTE call (VoLTE), the UE transmits a new voice packet at intervals of every 16 ms. Reverse link packets are transmitted in only four frames out of sixteen, with a resulting duty cycle of twenty-five percent, resulting in a 6 dB degradation in coverage for voice calls. The typical bandwidth of the voice decoder and encoder of a VoLTE call is 12.2 KHz. Therefore, assigning a minimum of 180 KHz of bandwidth to a telephone call is unnecessary and wastes resources.